This application is related to and claims priority from Japanese Patent Applications No. 2001-287312 filed on Sep. 20, 2001 and No. 2002-180153 filed on Jun. 20, 2002, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a refrigerant cycle system including first and second evaporators disposed in parallel. The refrigerant cycle system is suitably used for a vehicle air conditioner including a front air-conditioning unit for performing air-conditioning operation for a front seat area in a passenger compartment, and a rear air-conditioning unit for performing air-conditioning operation for a rear seat area in the passenger compartment.
2. Description of Related Art
Recently, the market request for a minivan has been increased. In the minivan, since the capacity of a passenger compartment is large, a vehicle air conditioner is required to have a large air-conditioning capacity. Therefore, in some minivans, a dual-type air conditioner, where an air-conditioning unit is individually disposed for each of the front and rear seat sides in the passenger compartment, is used. In a refrigerant cycle system used for the dual-type air conditioner, two evaporator are provided, respectively, for the front and rear seat sides in the passenger compartment while a common compressor and a common condenser are used. However, a low-pressure side refrigerant pipe of the rear evaporator is generally disposed under a vehicle floor, and is lower than a position of a refrigerant suction pipe of a compressor by a distance, for example, approximately 600 mm, in many cases. Therefore, a lubricating oil is stored in the low-pressure side refrigerant pipe at an outlet of the rear evaporator, and an amount of the lubricating oil returned to the compressor becomes short, thereby generating lubrication failure in the compressor, and reducing durability of the compressor.
JP-A-9-109656 proposes a refrigerant cycle system including a main evaporator mainly used as the front evaporator, and an assistant evaporator selectively used as the rear evaporator. The main evaporator and the assistant evaporator are disposed in parallel. In the refrigerant cycle system, when a compressor is continuously operated for a predetermined time in the single operation of the main evaporator, the operation of the compressor is forcibly interrupted by a predetermined frequency to change the low-pressure side refrigerant pressure at the refrigerant suction side of the compressor, so that it prevents oil returned to the compressor from being short due to the single operation of the main evaporator. Further, a variable displacement compressor is used as the compressor, and a discharge capacity of the compressor is forcibly changed when the compressor is continuously operated for the predetermined time in the single operation. However, in this refrigerant cycle system, there is not described regarding a control for preventing the oil return shortage when the compressor is operated with a small capacity. Accordingly, in this refrigerant cycle system, when the refrigerant amount discharged from the compressor is made small, the amount of the lubricating oil returned to the compressor may become insufficient.
Further, in the refrigerant cycle system, when an electric compressor is used as the compressor and the discharge capacity of the compressor is controlled by controlling a rotation speed of its motor, the amount of the oil returned to the compressor becomes short when the rotation speed of the motor is decreased for reducing the flow amount of refrigerant in the refrigerant cycle system.
The present invention has been made in view of the above-described problems, and its object is to provide a refrigerant cycle system which prevents an oil amount returning to a compressor from being insufficient due to a small flow amount of refrigerant discharged from the compressor.
According to the present invention, in a reference cycle system, a compressor for compressing and discharging refrigerant is a variable type in which a flow amount of refrigerant discharged from the compressor is variable, first and second evaporators into which refrigerant circulates by operation of the compressor are disposed in parallel, a first blower is disposed for blowing air to the first evaporator, and a second blower is disposed for blowing air to the second evaporator. In the refrigerant cycle system, a control unit for controlling the operation of the compressor includes determining means for determining whether the flow amount of refrigerant discharged from the compressor is in a low flow area when both the first blower and the second blower are operated at the same time. Further, the control unit has control means for forcibly switching the flow amount of refrigerant discharged from the compressor between a first state where the flow amount of refrigerant discharged from the compressor is smaller than a first value in the low flow area, and a second state where the flow amount of refrigerant discharged from the compressor is larger than a second value that is larger than the first value, when the operation state in the low flow area is continued for a predetermined time after the determining means determines that the flow amount of refrigerant discharged from the compressor is in the low flow area. Accordingly, even when both the first and second evaporators are operated, the operation state of the compressor in the low flow area of refrigerant is continued for the predetermined time, the operation of the compressor can be forcibly switched between the first state and the second state. Therefore, the refrigerant flow amount can be rapidly increased. Thus, even when lubricating oil is stored in a low-pressure side refrigerant pipe due to the small refrigerant flow amount, the lubricating oil stored in the low-pressure side refrigerant pipe can be effectively returned to the compressor.
Preferably, the flow amount of refrigerant discharged from the compressor is variable from a minimum flow amount to a maximum flow amount, and the first value is about the minimum flow amount, and the second value is about the maximum flow amount. Therefore, the refrigerant amount can be accurately rapidly increased, and the lubricating oil can be readily pushed by the rapidly increased refrigerant amount. More preferably, the control means switches the operation of the compressor between the first state and the second state by plural times at predetermined time intervals. Therefore, the lubricating oil staying in the low-pressure side refrigerant pipe can be effectively introduced into the compressor.
When the compressor is a variable displacement compressor in which a discharge capacity is variable, the flow amount of refrigerant discharged from the compressor is changed by changing the discharge capacity of the compressor, and the determining means determines the low flow area of refrigerant based on a control electrical current applied to the compressor. Alternatively, when the compressor is an electrical compressor including a motor and a compression mechanism that is driven by the motor, the flow amount of refrigerant discharged from the compressor is changed by controlling a rotation speed of the motor. Alternatively, the control unit controls the operation of the compressor to reduce the flow amount of refrigerant discharged from the compressor as a cooling load reduces, and the determining means determines the low flow area of refrigerant based on information relative to the cooling load.
Preferably, the first evaporator is a main evaporator that is mainly used, the second evaporator is an assistant evaporator that is selectively used, and control unit includes assistant control means for forcibly switching the flow amount of refrigerant discharged from the compressor between the first state and the second state, when a single operation state, where the first blower is singly operated and the second blower is stopped, is continued for a predetermined time after the compressor is operated. Accordingly, even when the first blower is singly operated while the second blower is stopped, it can prevent the lubricating oil from becoming insufficient in the compressor.
The first evaporator and the first blower can be disposed in a front air conditioning unit for performing air-conditioning operation of a front seat area in a passenger compartment of a vehicle, and the second evaporator and the second blower can be disposed in a rear air conditioning unit for performing air-conditioning operation of a rear seat area in the passenger compartment of the vehicle. Even in this case, the present invention can be effectively applied.